PolyU IR Community:
http://hdl.handle.net/10397/10
Wed, 30 Jul 2014 21:20:39 GMT2014-07-30T21:20:39ZNear-field beamformer design problems
http://hdl.handle.net/10397/6863
Title: Near-field beamformer design problems
Authors: Li, Zhibao
Abstract: This thesis is concerned with the near-field beamformer design problems in reverberant environment and the microphone array placement design problems. Firstly, we study the influence of room acoustics on the design of broadband beamformer. We introduce the image source method to estimate the room impulse responses, and establish several optimization models for the broadband beamformer design. We also study the barrier beamformer design problem, and introduce the space-time conservation element and solution element method to estimate the corresponding barrier impulse responses. Secondly, we study the time-domain beamformer design problem in the reverberant environment. We formulate the beamformer design problem as a linear system, and convert it into the least squares problem, whereas it has large scale and bad condition in the reverberant environment. Thus we introduce the Tikhonov regularization technique to improve the condition of the original problem. Moreover, we analyze the effectiveness of beamformer design as the filter length increases. With considering the nondirectional background noise of speech enhancement, the indoor LCMV beamformer problem is studied in the next. We use the estimated room impulse responses to formulate the model of indoor LCMV beamformer design, then construct a relaxed optimization problem to solve the filter coeffcients approximately. Moreover, post-filtering technique combining with indoor LCMV beamformer is studied to further improve the speech quality, and it is found that the MSIG post-filter combining with indoor LCMV beamformer has the best performance. Then we study the microphone array placement design problem, and formulate a composite optimization model for it. With the help of infinite length technique, we convert the subproblem on the solving of filter coefficients into the performance limit estimation problem. Moreover, we develop a hybrid descent method with genetic algorithm to solve the problem of microphone array placement design, the descent method can find the best solution around the current placement, and the genetic technique can jump out from the local solution. Finally, we study the microphone array placement design problem in reverberant environment. We introduce the LCMV framework combining with the infinite length technique to evaluate the effectiveness of placement design. And we also introduce the hybrid descent method to find the optimal array placement design eventually.
Description: xxii, 158 p. : ill. ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P AMA 2014 LiWed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10397/68632014-01-01T00:00:00ZStrong and weak convergence theorems for an infinite family of lipschitzian pseudocontraction mappings in banach spaces
http://hdl.handle.net/10397/6830
Title: Strong and weak convergence theorems for an infinite family of lipschitzian pseudocontraction mappings in banach spaces
Authors: Chang, Shih-sen; Wang, Xiong Rui; Lee, Heung-wing Joseph; Chan, Chi-kin
Abstract: The purpose of this paper is to study the strong and weak convergence theorems of the implicit iteration processes for an infinite family of Lipschitzian pseudocontractive mappings in Banach spaces.Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10397/68302011-01-01T00:00:00ZOptimal design of distributed microphone array
http://hdl.handle.net/10397/6773
Title: Optimal design of distributed microphone array
Authors: Gao, Mingjie
Abstract: This thesis concentrates on the study of distributed broadband beamforming system and source localization problem. The main contributions of this thesis consist of the following four parts. 1. For the design of distributed broadband beamforming system, each microphone is equipped with wireless communications capability. It is designed such that the error between the actual response and the desired response is minimized which is then formulated as a minimax optimization problem. Since we find that the performance of the optimized designs is very sensitive to the perturbations in microphone locations, we first use sensor network technology which solved by semi-definite programming method to estimate the microphone locations, and then incorporate it into the design process. We propose a suitable robust formulation as a remedy to regain the performance. The minimax optimization problem is transformed into a semi-definite programming problem so that interior point algorithms can be applied. We illustrate the proposed method by several designs and demonstrate that this approach is essential to regain accuracy in the optimized designs. 2. The broadband beamforming design problem is formulated as a non-strictly convex semi-infinite programming problem. The approach to solve it is that adding a small perturbation quadratic function to the objective function to make it strictly convex. We demonstrate that the solution of the per-turbation semi-infinite programming problem approximates the solution of the original problem as the perturbation going to 0. The new exchange algorithm is applied successfully to the filter design problem. 3. We present a new method to solve the source localization problem with time-difference information. Fist we formulate a mixed SDP-SOCP relaxation model and then state how to obtain the exact solution from the solutions of the mixed SDP-SOCP relaxation model and the second order polynomial equation. The estimator properties for the true source location under noises is proposed. We also give bi-level method to solve the source localization problem that formulated only as a semi-definite programming. Then a mixed SDP-SOCP relaxation model for source localization combined with sensor network localization problem is studied, also we give some statistical analyses for it. Many illustrated examples demonstrate those approaches can be applied successfully and some comparisons are presented. 4. We obtain a representation for the solution of the mixed SDP-SOCP model and the characterization such that the mixed SDP-SOCP model has an exact relaxation in two-dimensional case. We derive the geometry of the localizable region for the proposed mixed model. The characterization shows that the source localization with some time-difference information can be solved exactly by the mixed SDP-SOCP relaxation model in a larger region than the triangle region determined by three points.
Description: xiv, 163 p. : ill. ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P AMA 2013 GaoTue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10397/67732013-01-01T00:00:00ZHigher order positive semidefinite diffusion tensor imaging
http://hdl.handle.net/10397/6669
Title: Higher order positive semidefinite diffusion tensor imaging
Authors: Qi, Liqun; Yu, Gaohang; Wu, Ed X.
Abstract: Due to the well-known limitations of diffusion tensor imaging, high angular resolution diffusion imaging (HARDI) is used to characterize non-Gaussian diffusion processes. One approach to analyzing HARDI data is to model the apparent diffusion coefficient (ADC) with higher order diffusion tensors. The diffusivity function is positive semidefinite. In the literature, some methods have been proposed to preserve positive semidefiniteness of second order and fourth order diffusion tensors. None of them can work for arbitrarily high order diffusion tensors. In this paper, we propose a comprehensive model to approximate the ADC profile by a positive semidefinite diffusion tensor of either second or higher order. We call this the positive semidefinite diffusion tensor (PSDT) model. PSDT is a convex optimization problem with a convex quadratic objective function constrained by the nonnegativity requirement on the smallest Z-eigenvalue of the diffusivity function. The smallest Z-eigenvalue is a computable measure of the extent of positive definiteness of the diffusivity function. We also propose some other invariants for the ADC profile analysis. Experiment results show that higher order tensors could improve the estimation of anisotropic diffusion and that the PSDT model can depict the characterization of diffusion anisotropy which is consistent with known neuroanatomy.Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10397/66692010-01-01T00:00:00Z